Vacuum Insulation Panels – Exciting Thermal Properties and Most Challenging Applications

Vacuum insulation panels (VIPs) have a thermal resistance that is about a factor of 10 higher than that of equally thick conventional polystyrene boards. VIPs nowadays mostly consist of a load-bearing kernel of fumed silica. The kernel is evacuated to below 1 mbar and sealed in a highbarrier laminate, which consists of several layers of Al-coated polyethylene (PE) or polyethylene terephthalate (PET). The laminate is optimized for extremely low leakage rates for air and moisture and thus for a long service life, which is required especially for building applications. The evacuated kernel has a thermal conductivity of about 4×10−3 W·m−1 ·K−1 at room temperature, which results mainly from solid thermal conduction along the tenuous silica backbone. A U-value of 0.2W·m−2 ·K−1 results from a thickness of 2 cm. Thus slim, yet highly insulating fac¸ade constructions can be realized. As the kernel has nano-size pores, the gaseous thermal conductivity becomes noticeable only for pressures above 10 mbar. Only above 100 mbar the thermal conductivity doubles to about 8×10−3W·m−1 ·K−1, such a pressure could occur after several decades of usage in a middle European climate. These investigations revealed that the pressure increase is due to water vapor permeating the laminate itself, and to N2 and O2, which tend to penetrate the VIP via the sealed edges. An extremely important innovation is the iIntegration of a thermo-sensor into the VIP to nondestructively measure the thermal performance in situ. A successful “self-trial” was the iIntegration of about 100 hand-made VIPs into the new ZAE-building in W¨urzburg. Afterwards, several other buildings were super-insulated using